Thermal analysis and static strength of polyurethanes obtained from glycolysates

In this work thermal stability and tensile strength of polyurethanes obtained from glycolysates was investigated. The glycolysates were produced via glycolysis of waste polyurethane foam (PUR) in the reaction with 1,3-propylene glycol (PG). Polyurethanes were synthesized from the obtained intermediates by the prepolymer method using diisocyanate (MDI) and glycolysis product of molecular mass ranging from 700 to 1000, while 1,4-butylene glycol (BDO) was used as a chain elongation agent. The influence of NCO group concentration in prepolymer on tensile strength and elongation at break of polyurethanes was investigated using Zwick universal tensile tester. Thermal decomposition of the obtained glycolysates and polyurethanes was followed by TG coupled with FTIR spectroscopy. The main products of thermal decomposition have been identified.     

Synthesis and degradation profile of cast films of PPG-DMPA-IPDI aqueous polyurethane dispersions based on selective catalysts

Waterborne polyurethane (WBU) dispersions synthesized from poly(propylene glycol) (PPG), dimethylolpropionic acid (DMPA), and isophorone diisocyanate (IPDI) with catalysts of different selectivity were prepared via by the conventional prepolymer isocyanate process. Two types of chain extenders were used, ethylene glycol (EG) and propylene glycol (PG), producing polyurethanes. The dispersions were neutralized by the addition of triethylamine. The thermal stability of the materials, obtained as cast films prepared from aqueous dispersions was evaluated by thermogravimetry (TG). It was observed that initial degradation temperatures were above 140 °C, with two-step degradation profiles. The use of a more selective catalyst in the formulations led to materials with higher thermal stability. DTG curves exhibited stages not perceptible in the curves of weight loss, which were mainly influenced by the differences in the formulations. Thermal decomposition of the obtained polyurethanes was followed by TG coupled with FTIR spectroscopy.     

Kinetic model of poly(3-hydroxybutyrate) thermal degradation from experimental non-isothermal data

The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol⁻¹, logA=14.1±0.2 s⁻¹ for the kinetic model, and the autocatalytic model function was: f(α)=α^m(1−α)ⁿ=α^0.42(1−α)^0.56.     

Novel AB crosslinked polymer networks from telechelic 4‐vinylbenzyl carbamate terminated polyurethanes and different vinyl monomers

Novel AB crosslinked polymer (ABCP) networks were synthesized from telechelic 4‐vinylbenzyl carbamate terminated polyurethanes and monomers such as styrene, 4‐vinylpyridine, methyl methacrylate and butyl acrylate. Telechelic 4‐vinylbenzyl carbamate terminated polyurethanes were synthesized from polypropylene glycol‐based NCO‐terminated polyurethane and vinylbenzyl alcohol. Effect of changing the molecular weight of polypropylene glycol on the static and dynamic mechanical properties of ABCP networks from polyurethane‐polymethyl methacrylate was studied in detail. Dynamic mechanical thermal analysis results show that polymethyl methacrylate and polystyrene‐based ABCPs have good damping over a broad temperature range. ABCP networks prepared from 4‐vinylbenzyl carbamate terminated polyurethane and different monomers such as methyl methacrylate, butyl acrylate and styrene exhibit single tan δ_max value which implies excellent interlocking between the two polymers present in the ABCP networks. Static mechanical studies showed that methyl methacrylate and styrene‐based ABCP networks exhibit better tensile properties compared to other ABCP networks from butyl acrylate and 4‐vinyl pyridine monomers. Thermogravimetric analysis results revealed that the ABCP networks showed an improved thermal stability. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal behavior study and decomposition kinetics of salbutamol under isothermal and non-isothermal conditions

The thermal decomposition of salbutamol (β₂ — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage of the thermal decomposition process. For isothermal experiments the average values were E _act=130 kJ mol⁻¹ (for standard sample) and E _act=252 kJ mol⁻¹ (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min⁻¹). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min⁻¹). The calculated values were E _act=134 kJ mol⁻¹ (for standard sample) and E _act=139 kJ mol⁻¹ (for pharmaceutical sample).     

Thermally stable and flame‐retardant aromatic phosphate and cyclotriphosphazene‐containing polyurethanes: synthesis and properties

A novel flame retardant (4‐diphenylphosphoryloxyphenoxy)(4‐hydroxyphenoxy)cyclotriphosphazene (PPPZ) was prepared and characterized by FT‐IR, ³¹P‐NMR and ¹H‐NMR spectroscopy. Polyurethanes that contained aromatic phosphate groups attached to cyclotriphosphazene, with various phosphorus contents, were prepared from PPPZ, poly(propylene glycol), 1,4‐butanediol, and 2,4‐toluene diisocyanate by one‐step polymerization. The polymers prepared were characterized by FT‐IR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and oxygen index (LOI) measurements. The effect of the concentration of PPPZ on the thermal behavior of the polyurethane was studied. The results indicated that the glass transition temperature (T_g) of the polyurethane increased with the concentration of PPPZ. The PPPZ‐containing polyurethanes exhibited slightly higher temperatures of degradation and higher char yields than PPPZ‐free polyurethanes. Moreover, the LOI of the polyurethanes increased with increasing PPPZ content. Also studied was the possible mechanism of the flame retardancy. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of glycols used as glycolysis agents on chemical structure and thermal stability of the produced glycolysates

In this study, the influence of glycols on chemical structure and thermal stability of glycolysates as polyurethane intermediates were investigated. The intermediates were obtained by the glycolysis process of waste polyurethane foams in the reaction with different glycols ranging from ethylene glycol to hexane-1,6-diol. The used glycols were not separated from the product after the glycolysis process has been terminated. The effects of different weight ratio of glycols to polyurethane (PU) foam on chemical structure and thermal stability were investigated by FTIR, GPC, and TG/DTG. FTIR analysis of the glycolysates revealed their similar chemical architecture as manifested by the similarity of absorption peaks within the entire wavenumber range of spectra. This may indicate that the glycol has no influence on the chemical composition of glycolysates. GPC analysis showed that the glycolysates were characterized by polydispersity smaller than 2 which is lower as compared to some commercial polyols used for PU synthesis. GPC chromatograms showed that the applied glycols and the conditions of PU glycolysis allowed recreation of the original polyol as documented on the chromatograms by a single, well-formed peak at the beginning of retention time. Based on TG thermograms, it was established that glycol used in transesterification of PUs affected the temperature at which the loss of glycolysate mass by 5 and 10?% occurs. It was also observed that glycol affected the temperature at which the decomposition rate of glycolysates was the highest.     

Thermal and dynamic mechanical analysis of cross-linked poly(esterurethanes)

New cross-linked poly(esterurethanes) (PEU) based on unsaturated olygo(alkyleneester)diol (OAE), 4,4’-diphenylmethane diisocyanate (MDI) and styrene or methyl methacrylate as curing monomers were prepared. The synthesis of PEU was performed in two steps. In the first step OAE was obtained from adipic acid, maleic anhydride and ethylene glycol. In the second step a prepolymer was obtained in a reaction of OAE with different amounts of 4,4’-diphenylmethane diisocyanate followed by crosslinking using previously mentioned curing monomers. The influence of structure of the poly(esterurethanes) on thermal and dynamic mechanical properties is studied. Thermogravimetric analysis shows that cross-linked poly(esterurethanes) demonstrate high thermal stability. Moreover the dynamic mechanical thermal analysis shows that the presence of styrene cross-linking chains in polymers lead to the phase separation in cross-linked poly(esterurethanes).     

Thermoanalytical behaviour of carbaryl and its copper(II) and zinc(II) complexes

Non-isothermal techniques, i.e. thermogravimetry (TG) and differential scanning calorimetry (DSC), have been applied to investigate the thermal behaviour of carbaryl (1-naphthyl-N-methylcarbamate = 1-Naph-N-Mecbm) and its complexes, M(1-Naph-N-Mecbm)₄X₂, where M = Cu, X = Cl, NO₃ and CH₃COO and M = Zn, X = Cl. Carbaryl and Zn(1-Naph-N-Mecbm)₄Cl₂ complex exhibit two-stage thermal decomposition while the copper(II) complexes exhibit three and four-stage decomposition in their TG curves. The nature of the metal ion has been found to play highly influential role on the nature of thermal decomposition products as well as energy of activation ‘E*’. The presence of different anions does not seem to alter the thermal decomposition patterns. The complexes display weak to medium intensity exothermic and endothermic DSC curves, while the free ligand exhibits two endothermic peaks. The kinetic and thermodynamic parameters namely, the energy of activation ‘E*’, the frequency factor ‘A’ and the entropy of activation ‘S*’ etc. have been rationalized in relation to the bonding aspect of the carbaryl ligand. The nature and chemical composition of the residues of the decomposition steps have been studied by elemental analysis and FTIR data.     

Kinetics And Mechanism of The Non-isothermal Decomposition. Some Ni(II)-carboxylate-imidazole ternary complexes

The thermal decomposition of some Ni(II)-carboxylate-imidazole complexes in a nitrogen atmosphere was studied non-isothermally. From the non-isothermal thermoanalytical data, it was found that these complexes decompose through a stepwise release of imidazole molecules and/or CO ones forming unstable intermediates which produce metal oxide or the metal as a final decomposition product. TG in conjunction with DTG were used to evaluate the kinetic and thermodynamic parameters of the decomposition reaction. The kinetic studies were performed employing a computer-oriented kinetic analysis of each set of W-T data obtained under constant heating rate. The diffusion processes are the decisive mechanisms for the decomposition. The values of ΔE, A, ΔH, ΔS and ΔG for activation were calculated for the complexes and correlated to variation in their structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crystallization studies on linear aliphatic n‐polyurethanes

A detailed crystallization study of the linear n‐polyurethane (n‐PUR) family for n ranging from 5 to 12 was carried out by DSC supported by polarizing optical microscopy. The study embraces crystallization of all the n‐PUR under both nonisothermal and isothermal conditions. The odd and even series of n‐PUR defined by the parity of the number of methylenes (n) contained in the polymer repeating unit are considered and separately analyzed. All the members of the two series showed a thermal behavior consistent with their chemical constitution. Isothermal crystallization data were analyzed by the kinetics Avrami approach which revealed that the “crystallizability” of n‐PUR increases steadily with the flexibility of the polyurethane chain. Melting and enthalpy temperatures of isothermally and nonisothermally crystallized n‐PUR were found to vary with n according to a zig‐zag plot characteristic of odd–even effect. Given the structural similitude of n‐PUR with (n + 2)‐nylons, results were referenced to those reported for this family of polyamides. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1368–1380, 2009     

Thermal analysis study of imidazolinium and some benzimid azolium salts by TG

The imidazolinium and benzimidazolium bromide salts with pentafluor substituents on N atom were synthesized. The structures of imidazolinium and benzimidazolium bromide salts obtained were conformed by ¹H and ¹³C NMR, ¹⁹F NMR and elemental analysis. It was found that pyrolytic decomposition occurs with melting in salts. The imidazolinium and benzimidazolium bromide salts were studied by TG-DTG and DTA from ambient temperature to 1000°C in nitrogen atmosphere. The decomposition occurred mainly in one stage and the values of activation energy E, frequency factor A, reaction order n, enthalpy change ΔH ^#, entropy change ΔS ^# and Gibbs free energy ΔG ^#, of the thermal decomposition were calculated by means of Coats-Redfern (CR), MacCallum-Tanner (MC) and van Krevelen (vK) methods. The activation energy value obtained by CR and MC methods were in good agreement with each other while those obtained by vK were found to be 10–12 kJ mol⁻¹ larger.     

Mechanism of thermal degradation of polyurethanes investigated by direct pyrolysis in the mass spectrometer

Direct pyrolysis in the mass spectrometer (MS) yielded unequivocal evidence regarding the mechanism of thermal decomposition of N-monosubstituted and N-disubstituted polyurethanes. It was ascertained that direct pyrolysis in the MS detects the primary thermal fragments that originate from polyurethane pyrolysis. This is particularly useful when, as in the thermal decomposition illustrated in eq. (1), it is necessary to distinguish between primary and secondary thermal fragments in order to assess the thermal degradation mechanism. Our results indicate that N-monosubstituted polyurethane V undergoes a quantitative depolycondensation process. Instead, the thermal decomposition of the N-disubstituted polyurethane VI which occurs selectively in eq. (1) is demonstrated by the detection of thermal fragments that contain secondary amine and olefinic end groups. Finally, polyurethane VI shows a higher thermal stability with respect to polymer V because of the absence of the depolycondensation process, which accounts for the thermal degradation of the N-monosubstituted polyurethane V.     

Thermal studies on polymorphic structures of tibolone

Tibolone polymorphic forms I (monoclinic) and II (triclinic) have been prepared by recrystallization from acetone and toluene, respectively, and characterized by different techniques sensitive to changes in solid state, such as polarized light microscopy, X-ray powder diffractometry, thermal analysis (TG/DTG/DSC), and vibrational spectroscopy (FTIR and Raman microscopy). The nonisothermal decomposition kinetics of the obtained polymorphs were studied using thermogravimetry. The activation energies were calculated through the Ozawa’s method for the first step of decomposition, the triclinic form showed a lower E _a (91 kJ mol⁻¹) than the monoclinic one (95 kJ mol⁻¹). Furthermore, Raman microscopy and DSC at low heating rates were used to identify and follow the thermal decomposition of the triclinic form, showing the existence of three thermal events before the first mass loss.     

Comparative kinetic study of decomposition of some diazepine derivatives under isothermal and non-isothermal conditions

Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances. TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability, compatibility, polymorphism, kinetic analysis, phase transitions etc.). The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric kinetics. In the model-fitting methods the kinetic triplets (f(α), A and E _a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous work. The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as well as a different strategy of experimental data processing.     

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of thermal decomposition of CeO2 nanocrystalline precursor prepared by precipitation method

The thermal decomposition of CeO₂ nanocrystalline precursor prepared by chemical precipitation method was investigated using thermo-gravimetric/differential scanning calorimetry (TG/DSC) and X-ray powder diffraction (XRD). In particular, the differential thermal analysis curves for the decomposition of CeO₂ nanocrystalline precursor were measured at different heating rates in air by a thermal analyzer (NETZSCH STA 449C, Germany). The kinetic parameters of the thermal decomposition of CeO₂ nanocrystalline precursor were calculated using the Kissinger method and the Coats-Redfern method. Results show that the apparent active energy E of the reaction is 105.51 kJ/mol, the frequency factor lnA is 3.602 and the reaction order n is 2. This thermal decomposition process can be described by the anti-Jander equation and a three-dimensional diffusion mechanism. Tanslated from Journal of Central South University (Science and Technology), 2007, 38(3): 428–432 [译自: 中南大学学报(自然科学版]     

Thermal stability and degradation of Co(II), Cd(II), and Zn(II) complexes with <Emphasis Type="Italic">N</Emphasis>-benzyloxycarbonylglycinato ligand

Thermal behavior of Co(II), Cd(II), and Zn(II) complexes with N-benzyloxycarbonylglycinato ligand was investigated using the results of TG, DSC and DTG analysis obtained at different heating rates (2.5 to 30 °C min⁻¹), from room temperature to about 900 °C. Mechanisms of complex degradation, as well as enthalpies of the degradation processes were determined. It is shown that thermal stability of investigated complexes correlates with their crystal structures, especially with the presence of crystallization and coordinated water molecules. The values of dehydration enthalpies are discussed and correlated with composition of the complexes. Kissinger’s, Ozawa’s, and Friedman’s isoconversion methods were used for the determination of kinetic parameters: the pre-exponential factor A and the apparent activation energy E _a. For all three complexes and all steps of degradation, the values of kinetics parameters obtained by Kissinger’s and Ozawa’s methods are in good agreement. The results obtained by Friedman’s method showed that some decomposition steps are simple and some others are complex ones.     

Thermal investigation of strontium acetate hemihydrate in nitrogen gas

The thermal decomposition of strontium acetate hemihydrate has been studied by TG-DTA/DSC and TG coupled with Fourier transform infrared spectroscopy (FTIR) under non-isothermal conditions in nitrogen gas from ambient temperature to 600°C. The TG-DTA/DSC experiments indicate the decomposition goes mainly through two steps: the dehydration and the subsequent decomposition of anhydrous strontium acetate into strontium carbonate. TG-FTIR analysis of the evolved products from the non-oxidative thermal degradation indicates mainly the release of water, acetone and carbon dioxide. The model-free isoconversional methods are employed to calculate the E _a of both steps at different conversion α from 0.1 to 0.9 with increment of 0.05. The relative constant apparent E _a values during dehydration (0.5<α<0.9) of strontium acetate hemihydrate and decomposition of anhydrous strontium acetate (0.5<α<0.9) suggest that the simplex reactions involved in the corresponding thermal events. The most probable kinetic models during dehydration and decomposition have been estimated by means of the master plots method.